It is known that the content of only an insignificant amount of moisture, gases and products of ageing, which are produced both during use and in the process of storage, is permissible in insulating and other petroleum mixtures when they are used. This relates both to new oils ready for use and to mixed oils, and also to oils used in high-voltage apparatuses such as power and measuring transformers, high-voltage switches, etc. An increase in the content of the aforesaid substances above the permissible values more often than not is a consequence of unsuitable conditions for storage and use. And in insulating oil in high voltage apparatuses, furthermore, this is a consequence of ageing of oil-paper insulation, wherein this process accelerates in time. The process of ageing is that under the effect of heated conductors, and also in the presence of ferromagnetic transformer steel, the polymerized molecules of cellulose insulation decompose and oxidize the oil molecules. The products of ageing pass from the paper insulation into the oil and as catalysts provide for a high level of oxidation until acids appear. Wherein the degraded oil acts on the cellulose of the insulation and accelerates the process of ageing. Simultaneously, the presence of moisture in insulating oils substantially reduces their dielectric constant, which is the most important characteristic of the oils used in high-voltage apparatuses.
Apparatuses with filters and vacuum chambers for degassing and dehydrating oil are known in engineering practice. Centrifugal equipment with chambers for degassing and dehydrating is also known.
A drawback of the aforesaid known apparatuses with filters and vacuum chambers is that when gases and dissolved water are extracted in a high vacuum from the oil, easily evaporating fractions of petroleum are also removed, which impairs the quality of the processed oil. Furthermore, the complexity of the equipment and of the process of its operation should also be listed as drawbacks.
The relative complexity of the equipment and significantly higher consumption of adsorbents, especially during the processing of highly degraded oils of old transformers, should be indicated as drawbacks of centrifugal equipment with chambers for degassing and dehydrating with adsorbents. A separate problem here is how to get rid of contaminated adsorbents after their use, since they are refuse with carcinogenic properties.
A method of filtering mineral oils and an apparatus for carrying out the method are known and disclosed in Yugoslavian patent No. 26744. Filtering and dehydrating an oil mixture in that known apparatus are carried out using filters comprising a layer of sodium chloride having a thickness of about 100 mm. Wherein the emulsion being processed passes through an N 3 sieve at a positive pressure of about 29.4 kPa and linear flow rate of 5.times.10.sup.-2 m/s. The emulsion passing through the capillary barriers contacts with the filtering layer. As a consequence thereof the dispersed phase loses kinetic energy, and its concentration in a certain cross section of the filtering layer rises. Since therewith dehydration of the dispersed particles also takes place, they can be removed due to precipitation into a residue.
Among the drawbacks of this known solution is the low efficiency of purification of the oils being processed. It does not ensure the required degree of filtration, degassing, dehydration and removal of products of ageing in insulation oils during one cycle of running the oil through the filterng component.
A method of filtering and a filter with an ion-exchanger for carrying out the method are also known and disclosed in Yugoslavian patent No. 29045. In this patent provision is made for the possibility of regenerating the filter without moving and removing the active component. For this an elastic bag of the blacksmith bellows type, which swells during regeneration of the filter and presses against the surface of the active component when liquid is passed through the filter for regeneration, is positioned above a layer of active filtering material disposed on top of a corresponding sieve. This liquid flows in the opposite direction, without bringing about a change in the structure of the active component which is freed from the particles restrained during filtering.
The aforesaid drawbacks, which on the whole can be characterized as insufficient efficiency of purification of the oils being processed and of regeneration of the active component when it is saturated, are also characteristic for that known solution.